The invention relates to a delivery system for delivery and deployment of a stent, to a desired vascular location.
Vascular intervention is today undertaken to treat a large number of diseases that had heretofore been treated by surgery. Stents are used widely in a number of applications to provide structural support to vessels that are being treated. Typically, a vascular intervention procedure is required to restore the flow of blood through an artery that has been constricted by a build up of atherosclerotic material. Medical practice has shown that implanting stents at the site of disease is effective. Various types of stents have been devised and the therapy is well known and widely practised.
Stent designs are broadly divided into two categories, balloon expandable stents and self-expanding stents. The invention relates particularly to the delivery and positioning of self-expanding stents. The term self-expanding refers to the inherent material properties of the stent which cause the expansion of the stent once an external constraint has been removed. The effect is most commonly achieved by using a shape memory metallic alloy such as nitinol.
Generally, stents are delivered to the desired location by means of a catheter, specifically referred to as a delivery catheter. Delivery catheters are threaded through a guiding catheter to the site of the disease and once the correct position has been established by means of fluoroscopic or other imaging method, the stent is deployed.
There is however a problem with conventional stent delivery systems in that it is difficult and time consuming to deploy stents. A full length over the wire catheter is used in combination with an exchange length guidewire over which the delivery catheter is manipulated. Such systems are cumbersome to handle and a second operator is generally required to assist the lead clinician in controlling the procedure. When the guidewire is positioned at the commencement of the procedure, it is desirable that it""s position is stable during the remainder of the procedure as it provides access to the treatment site for the therapeutic or diagnostic devices used in treatment. If it is desirous to insert or exchange a catheter, it is necessary to thread the catheter over the guidewire while retaining control of the guidewire. This is achievable only if the length of available guidewire outside the body is greater than the length of the catheter being loaded. Intravascular catheters typically measure 1.3 metres or more. It is impossible for one clinician to maintain position and control of a guidewire and simultaneously thread on a catheter more than a metre away.
There is therefore a need for a delivery catheter system which will overcome at least some of these difficulties.
According to the invention there is provided a stent delivery catheter for delivery and deployment of a stent comprising:
an elongate catheter body;
a self-expanding stent overlying said catheter body at a distal end thereof;
a sheath overlying said stent to constrict the stent during delivery;
the catheter body having a guidewire lumen with a guidewire exit at a distal end of the catheter body and a guidewire entrance proximal of the stent;
a guidewire extending through the lumen between the guidewire entrance and the guidewire exit; and
stent deployment means comprising means for moving the sheath relative to the catheter body to release the stent;
the sheath having guidewire accommodating means for accommodating the guidewire so that the guidewire entrance is not obstructed during movement of the sheath relative to the catheter body.
Most preferably the guidewire accommodating means is an opening in the sheath which is arranged to align with the guidewire entrance to prevent obstruction of the entrance on deployment of the stent.
Preferably the guidewire accommodating means is configured to correspond with the operation of the stent deployment means.
In a preferred arrangement the sheath opening has a length which is greater than or equal to the length of the stent to be deployed.
Ideally the sheath opening comprises an elongate slot.
Preferably the stent deployment means is a linear actuating means. In a preferred arrangement the actuating means includes converter means for converting rotational movement of an actuator into linear motion to move the sheath linearly.
Preferably the converter means comprises a shuttle which is linearly movable within a shuttle guide, on rotation of the actuator.
Ideally the shuttle screw threadingly engages the actuator. Preferably the thread has at least two starts. Ideally, the thread is a four start thread.
In one embodiment of the invention the actuator is a shuttle nut. Preferably the shuttle nut includes an operator handle. The operator handle may be a knurled portion of the shuttle nut.
In a particularly preferred arrangement the shuttle has at least two wings and the guide includes corresponding slots to substantially prevent rotation of the wings on rotation of the actuator. The oppositely directed wings have the effect of stabilising the shuttle in the guide slots.
A shuttle shaft preferably is connected to and extends forwardly of the shuttle. The shuttle shaft thereby provides an extension of the shuttle. Preferably the sheath is attached to the shuttle shaft.
The actuating means may comprise a threaded shaft and an associated thumbwheel which is rotated to move the shaft linearly. An anti-rotation means to control rotation of the threaded shaft is preferably provided. The thread on the shaft may be discontinuous. Ideally the thread is a multistart thread, preferably a four start thread.
In another arrangement the restraining sheath is slit helically at one or more circumferential location such that a combined linear and rotational motion of the sheath will maintain the opening for the guidewire to pass freely.
Preferably the stent deployment means is attached to the sheath. Typically, the actuating means includes a pull wire attached directly or indirectly to the sheath.
The invention also provides a constriction sheath for use with a delivery catheter of the invention. The constriction sheath has an opening which may be arranged to align with the guidewire lumen entrance to prevent obstruction of the entrance on movement of the constriction sheath.
In a particularly preferred arrangement the opening is an elongate slot having a length which is greater than or equal to the length of a stent to be deployed.
The invention further provides a catheter for deploying a stent, the catheter having a pathway extending longitudinally and in parallel with a coaxial guidewire to permit free movement of the guidewire and providing a path for a stent release means.
Thus, the invention provides a means for rapidly deploying a self-expanding stent by way of a pull or push motion of the sheath without interference with any guidewire path.
The invention also provides a restraining sheath that is slit longitudinally at one or more circumferential location such that linear motion of the sheath will maintain the opening for the guidewire to pass freely.
The invention further provides a restraining sheath that is slit helically at one or more circurmfrential location such that a combined linear and rotational motion of the sheath will maintain the opening for the guidewire to pass freely.
The invention further provides a rapid exchange stent delivery catheter having a pathway extending longitudinally and in parallel with a coaxial guidewire to permit movement of the guidewire and providing a path for a pull wire or suture used to release a stent restraining sheath.